Process for preparing sulfuryl-fluoride and -chlorofluoride products

ABSTRACT

A product mixture resulting from the reaction of an anhydrous gaseous mixture of sulfur dioxide, chlorine and hydrogen fluoride in the presence of a catalyst is heated at a temperature of at least about 35° C. under pressures up to about 65 psi to effect substantial conversion of undesired free chlorine in the resulting product mixture to sulfuryl chlorofluoride. The conversion of free chlorine to sulfuryl chlorofluoride allows the use of a completely anhydrous process from which uncontaminated sulfuryl fluoride and sulfuryl chlorofluoride products can readily be obtained. A method for the production of sulfuryl chlorofluoride from said gaseous mixture is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 616,517 filed Sept. 25,1975 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a process for the recovery of sulfurylfluoride and sulfuryl chlorofluoride substantially free of undesiredchlorine contaminant. In accordance with another aspect, this inventionrelates to a method of preparing sulfuryl chlorofluoride from a reactionmixture of sulfur dioxide, chlorine and hydrogen fluoride.

The preparation of sulfuryl fluoride (SO₂ F₂) from an anhydrous gaseousmixture of sulfur dioxide (SO₂), chlorine (Cl₂) and hydrogen fluoride(HF) in the presence of a catalyst at temperatures of from about 150 toabout 450° C., preferably above about 200° C., is conventional in theart. U.S. Pat. Nos. 2,772,144, 3,092,458, and 3,320,030 all relate tosuch manufacture of SO₂ F₂ while U.S. Pat. No. 2,875,127 relates to theuse of SO₂ F₂ as a fumigant. It is the usual prior art practice to passthe SO₂ F₂ product reaction mixture exiting from a reactor through anaqueous scrubber system to recover many of the undesired by-products orunused reactants, e.g., Cl₂, SO₂, HCl and SO₂ ClF, before recovering thefinal product. The presence of free chlorine in the final product isundesired in view of its highly corrosive nature; such free chlorinecannot readily be distilled from the desired product in view of theazeotrope mixture that Applicants believe forms with sulfuryl fluorideand the use of aqueous scrubbers taught in the art is unsatisfactory asthey do not completely remove the free chlorine content. Moreover, thesemethods suffer other disadvantages on account of numerous attendantpollution problems associated with such aqueous effluent waste streams,as well as the economic loss of valuable unused reactants and hydrogenchloride by-product.

The production of SO₂ ClF by reacting SO₂, HF and Cl₂ in the presence ofactivated carbon catalyst and an alkali metal bifluoride at 100°-200° C.is also taught by the U.S. Pat. No. 3,320,030 mentioned above. Variousother processes utilizing different reactants, e.g., KSO₂ F and Cl₂, SO₂Cl₂ and SbF₃, CoF₃, AgF₂, MnF₃, NH₄ F, NH₄ HF₂ and the like are alsotaught in the art but are not considered as pertinent as the teachingsof the U.S. Pat. No. 3,320,030.

Accordingly, an object of this invention is to provide an improvedprocess whereby SO₂ F₂ substantially free of chlorine can be obtainedwithout the employment of aqueous scrubbing systems.

Another object of the present invention is to provide a method wherebySO₂ ClF can be produced from excess chlorine contained in an SO₂ F₂product reaction mixture.

Other objects and aspects, as well as several advantages of theinvention, will become apparent upon consideration of the accompanyingdisclosure and the appended claims.

SUMMARY OF THE INVENTION

Unexpectedly, it has been found that if a product reaction mixtureresulting from the contacting of sulfur dioxide, chlorine and hydrogenfluoride in the presence of an activated charcoal catalyst is subjectedto further reaction, undesired free chlorine present in the productreaction mixture and in the desired final product, SO₂ F₂, can besubstantially eliminated. Thus, in accordance with one embodiment of theinvention, a process is provided wherein a product mixture, comprisingsulfuryl fluoride and resulting from the reaction of an anhydrousgaseous mixture of sulfur dioxide, chlorine and hydrogen fluoride in thepresence of a catalyst comprising activated carbon, is reacted at areaction temperature of at least about 35° C. and reaction pressures offrom atmospheric to about 65 psi in the presence of a catalystcomprising activated carbon, thereby reducing the free chlorine contentof said mixture by converting the same to sulfuryl chlorofluoride.

In accordance with another embodiment of the invention, the resultingSO₂ ClF is recovered from the SO₂ F₂ product mixture. In still anotherembodiment, SO₂ F₂ substantially free of chlorine is separated from theproduct mixture.

In another embodiment of the invention, it has unexpectedly been foundthat an anhydrous gaseous mixture of SO₂, Cl₂ and HF can be reacted, inthe presence of a catalyst comprising activated carbon, directly to asubstantially chlorine free SO₂ ClF product under the conditions of thepresent invention with little or no formation of SO₂ F₂.

Advantageously, the present invention provides a completely anhydrousprocess by which SO₂ F₂ and SO₂ ClF can be continuously producedsubstantially free of Cl₂, thus obviating the steps of productpurification by conventional aqueous recovery methods.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is not dependent upon specific reaction conditionsconcerning the initial formation of the SO₂ F₂ containing productreaction mixture from which undesired free chlorine is to be removed.These conditions are generally well known in the art as set forth in theBackground herein. Generally, the product reaction mixture comprisingSO₂ F₂ as prepared by the prior art methods also contains SO₂, HF, HCland undesired free Cl₂. A typical such product reaction mixture isprepared by reacting an anhydrous mixture of about 1.0 mole Cl₂, about1.35 mole SO₂ and from 2.5 to about 4.5 mole HF. The product reactionmixture thus obtained usually comprises 1.0 mole SO₂ F₂, 0.35 mole SO₂,up to about 2.5 mole HF and varying amounts, e.g., from 50 to about10,000 ppm or more of free Cl₂. The amount of undesired free Cl₂ mayvary considerably depending upon the condition of the carbon catalystand the amount of Cl₂ initially used. As used herein, the term "Cl₂removal" is understood to be synonymous with "Cl₂ conversion to SO₂ClF".

Such undesired excess chlorine is substantially, if not completely,reduced by the method of the present invention wherein the SO₂ F₂product reaction mixture containing free Cl₂ is further reacted over acatalyst comprising activated carbon. Whether or not the excess Cl₂exists as free excess chlorine per se in the product reaction mixture oras SO₂ Cl₂ is not definitely known. However, SO₂ Cl₂ readilydisassociates to SO₂ and Cl₂ or reacts in analysis methods as SO₂ Cl₂and substantially all of the Cl₂ can, within the limits of detection,irrespectively be removed.

The minimum reaction temperature employed to obtain substantial Cl₂removal may range from about 35° to about 145° C., the exact reactiontemperature being dependent upon the reaction pressures and feed ratesemployed. Reaction pressures of from atmospheric to about 65 psi aretypically employed. Usually, a pressure of at least about 1-2 psi isemployed to move the reaction mixture through the reactor. It has alsobeen observed that, as the reaction pressure is increased, the reactiontemperature must likewise be increased in order to maintain substantialconversion of the free Cl₂ to SO₂ ClF. Thus, at reaction pressures nearatmospheric and a reaction temperature of about 35° C., the minimumreaction temperature must generally be increased about 10° C. for everyincrease of from about 6 to 8 psi in order to maintain the recovery ofSO₂ F₂ and/or SO₂ ClF products substantially free of Cl₂. Thus, forexample, at pressures slightly above atmospheric, e.g., 1-2 psi, theminimum temperature required to maintain substantial, if not complete,removal of Cl₂ is about 35-40° C. Temperatures of from about 35 to aboutas high as 100° C. at this pressure range can be employed andsubstantial removal of Cl₂ obtained. However, at such pressures, theremoval of Cl₂ begins to decrease as the temperature is increased toabove about 100° C. The maximum temperature which can be employed toaccomplish substantial removal of Cl₂ may thus be higher than theminimum required temperature at a given pressure. Generally, however,the range between the minimum and maximum temperatures whereinsubstantial Cl₂ removal is obtained will decrease due to reactionkinetics as the operating pressures are increased, the maximumtemperature being limited to approximately 145° C. at about 65 psi. Theexact minimum and maximum temperatures can, of course, be readilydetermined by test runs using the Cl₂ analysis methods as hereinafterset forth. Temperatures above or below the maximum or minimumtemperatures can, of course, be utilized where the presence of free Cl₂in the SO₂ F₂ or SO₂ ClF products can be tolerated.

For the purposes of the present invention wherein substantial Cl₂removal by conversion thereof to SO₂ ClF is desired, and where SO₂ F₂and/or SO₂ ClF products free of Cl₂ are desired, minimum temperatures offrom about 35 to about 145° C. and pressures of from about atmosphericto about 65 psi can be employed. Economic considerations in plantconstruction, etc., dictate that lower pressures ordinarily be utilized.In a preferred embodiment, minimum reaction temperatures of from 40 toabout 120° C. at pressures of from atmospheric to about 50 psi areemployed. In another preferred embodiment, minimum reaction temperaturesof from about 40° to about 100° C. at pressures of from about 2 to about37 psi are employed.

Any of the commercially available activated carbons may be employed ascatalysts in the present invention. Advantageously, the process of thepresent invention effectively converts excess Cl₂ to SO₂ ClF with littleapparent effect on the catalyst employed.

Another consideration involved in the practice of the present inventionis residence or contact time. Those skilled in the art recognize thatthis element is highly variable depending upon such other factors asreaction temperature, type of apparatus, overall size of a specificoperation and the like. For any particular operation with givenapparatus equipment, determination of process variables such as optimumreaction temperature, pressure and contact time is within the skill ofthe art, and may be determined by test run.

Generally, the contact time can be from about 1 to 10 or more seconds.Preferably, the contact time of the claimed process is about one-halfthe contact time of the initial reactants used to prepare the SO₂ F₂containing reaction mixture. A preferred contact time is from about 1 toabout 4 seconds.

Apparatus constituting the reactor and related accessories are simpleand, along with the product recovery systems following the reactor, maybe along the lines described in the appended examples. Those skilled inthe art will readily recognize such equipment, as well as otherconventional equipment set forth in the references cited in theBackground herein which can be employed for the purposes of the presentinvention. While a second reactor, essentially the same as the firstreactor used to react SO₂, Cl₂ and HF to a product reaction mixturecontaining SO₂ F₂, is conveniently employed, the use of a single reactorto accomplish both the formation of SO₂ F₂ and the removal of Cl₂ fromsuch product mixture containing SO₂ F₂ to form SO₂ ClF is within thescope of the present invention.

The process of the present invention can be monitored with respect tothe removal of Cl₂ and the production of SO₂ ClF by analysis of thegaseous mixture obtained from the reaction. In such operations, a sampleof the gaseous mixture is reacted with a propylene and nitrogen mixtureand the resulting mixture analyzed by gas phase chromatography forpropylene dichloride, which will be formed by reaction with excess Cl₂or SO₂ Cl₂ present. Amounts as low as about 50 ppm Cl₂ can be detectedby such analysis method.

The following examples illustrate practice of the invention.

EXAMPLE 1

A 10 inch long, three-fourth inch diameter Hastelloy C reactor tube waspacked with 9 × 10 mesh PCB coconut charcoal and maintained at atemperature of about 180° C. An anhydrous gaseous mixture comprisingabout 1.0 mole Cl₂, about 1.35 moles SO₂ and about 4.5 moles HF wasmetered thereto at about 12 psi with an average contact time of themixture in the reactor of about 5 seconds. The product reaction mixturecomprising SO₂ F₂, SO₂, HF and HCl in mole ratios of about 1.0: .35 :2.5 : 2.0 and containing detectable amounts of Cl₂ and/or SO₂ Cl₂ wasfed into a second similar 5" × 3/4" packed reactor. The temperature ofthe second reactor was about 65° C. and the pressure was about 12 psi.The product reaction mixture contact time in the second reactor wasabout 2.5 seconds.

Analysis of the mixture exiting the second reactor indicated thepresence of SO₂ F₂, HCl, SO₂, HF and SO₂ ClF. Reaction of the mixtureexiting the second reactor with propylene diluted with nitrogen andanalysis of the resulting mixture for propylene dichloride content bymeans of gas phase chromatography was carried out. Within the limits ofdetection of the analytical method, no propylene dichloride was found,indicating the absence of Cl₂ or SO₂ Cl₂ in the product mixture.

EXAMPLE 2

Utilizing equipment and procedures as in Example 1, the product reactionmixture exiting the first reactor was reacted at about 43° C. and about2 psi for a period of about 2.5 seconds. The gaseous product mixtureexiting the second was similarly analyzed with no detectable Cl₂ beingfound.

In similar operations, it was found that SO₂ F₂ products having nodetectable Cl₂ levels could be obtained at temperatures of from about 43to about 100° C. at a pressure of about 2 psi.

EXAMPLE 3

In other operations utilizing a 20 foot long, 2-inch diameter HastelloyC reactor tube packed with 4 × 10 mesh PCB coconut charcoal catalyst,typical SO₂ F₂ containing reaction mixtures therefrom having from 2000to 3000 or more ppm Cl₂ have been found to have no detectable Cl₂ or SO₂Cl₂ levels after treatment in a second similar reactor of 10 feet inlength and being operated at about 100° C. and about 35 psi.

EXAMPLE 4

A first reactor similar to that described in Example 1 above but havingan inactive catalyst producing little or no SO₂ F₂ from the reaction ofCl₂, SO₂ and HF and producing a product reaction mixture containing someSO₂ ClF and high amounts, i.e., about 20,000 ppm of Cl₂ at about 180° C.and 2 psi was utilized to determine the effect of temperature andcatalyst conditions on the removal of Cl₂. In such operations, thereactor was operated at lower temperatures of about 100° C. at 2 psi anda similar gaseous mixture of about 1.0 mole Cl₂, 1.35 mole SO₂ and about4.5 mole HF being fed thereto. The gaseous mixture exiting therefrom wasanalyzed and found to have no detectable Cl₂ or SO₂ Cl₂ and fullconversion to SO₂ ClF. Such results clearly indicate the effectivenessof the present process for preparing a substantially Cl₂ free SO₂ ClFproduct from SO₂, HF and Cl₂ and demonstrate that a long catalyst lifefor the process could be expected.

Data from various other runs with other similar equipment confirm theeffectiveness of the process in Cl₂ removal and conversion to SO₂ ClF.

Various modifications may be made in the process of the presentinvention without departing from the spirit or scope thereof and it isto be understood that we limit ourselves only as defined in the appendedclaims.

We claim:
 1. A process for removing chlorine from a product reactionmixture comprising sulfuryl fluoride and prepared by the reaction of ananhydrous gaseous mixture of sulfur dioxide, chlorine and hydrogenfluoride in the presence of a catalyst comprising activated carbon, saidprocess comprising reacting the product reaction mixture at atemperature of from about 35° to about 145° C. and at a pressure of fromabout atmospheric to about 65 psi in the presence of a catalystcomprising activated carbon, thereby reducing the free chlorine contentof said mixture and converting free chlorine present in said productreaction mixture to sulfuryl chlorofluoride and thereafter separatingSO₂ F₂ from the product reaction mixture.
 2. The process of claim 1wherein sulfuryl chlorofluoride is recovered from the product mixture.3. The process of claim 1 wherein the sulfuryl fluoride productrecovered contains no detectable levels of free chlorine.
 4. The processof claim 3 wherein the sulfuryl chlorofluoride product recoveredcontains no detectable levels of free chlorine.
 5. The process of claim1 wherein the pressure range is from about atmospheric to about 50 psiand the reaction temperature range is from about 40 to about 120° C. 6.The process of claim 1 wherein pressures of from about 2 to about 37 psiare employed and the reaction temperature range at such pressures isfrom about 40 to about 100° C.
 7. The process as defined in claim 1wherein the anhydrous gaseous mixture comprises about one mole ofchlorine, about 1.35 moles of sulfur dioxide and about 4.5 moles ofhydrogen fluoride and wherein the product reaction mixture comprisesabout 1 mole of sulfuryl fluoride, about 0.35 moles of sulfur dioxide,about 2.5 moles of hydrogen fluoride, about 2 moles of hydrogen chlorideand free chlorine.